Re: Tips on building a stash. I do primarily 2 different things.
#1 is where I have a particular quilt pattern that I plan to use and buy fabrics just for that quilt; I always buy extra yardage in case of errors, plus leftovers are always welcome in my quilt stash. (I'm a bit physically uncoordinated, so I sometimes make really stupid errors.)
#2 (and this is really the best "stash builder") is that when I see something I really like, I buy it. When I'm ready to use these fabulous fabric finds, I cut small strips from them and use those strips at the fabric store to find coordinating fabrics.
More often then not, I buy fabric first and plan the quilt tops later. I very rarely pay full price for fabric; if I don't have a coupon or it's not on sale, I usually don't buy it.